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Network Working Group Request for Comments: 3923 Category: Standards Track |
P. Saint-Andre Jabber Software Foundation October 2004 |
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright © The Internet Society (2004).
This memo defines methods of end-to-end signing and object encryption for the Extensible Messaging and Presence Protocol (XMPP).
1. Introduction
2. Requirements
3. Securing Messages
4. Securing Presence
5. Securing Arbitrary XMPP Data
6. Rules for S/MIME Generation and Handling
7. Recipient Error Handling
8. Secure Communications Through a Gateway
9. urn:ietf:params:xml:xmpp-e2e Namespace
10. application/xmpp+xml Media Type
11. Security Considerations
12. IANA Considerations
13. References
A. Schema for urn:ietf:params:xml:ns:xmpp-e2e
Author's Address
Full Copyright Statement
This memo defines methods of end-to-end signing and object encryption for the Extensible Messaging and Presence Protocol (XMPP). (For information about XMPP, see [XMPP-CORE] and [XMPP-IM].) The method specified herein enables a sender to sign and/or encrypt an instant message sent to a specific recipient, sign and/or encrypt presence information that is directed to a specific user, and sign and/or encrypt any arbitrary XMPP stanza directed to a specific user. This memo thereby helps the XMPP specifications meet the requirements specified in [IMP-REQS].
This document inherits terminology defined in [CMS], [IMP-MODEL], [SMIME], and [XMPP-CORE].
The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [TERMS].
For the purposes of this memo, we stipulate the following requirements:
We further stipulate that the following functionality is out of scope for this memo:
In order to sign and/or encrypt a message, a sending agent MUST use the following procedure:
<e2e/> child of a <message/> stanza, where the <e2e/> element is
qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace as
specified more fully in Section 9 below.
The following example illustrates the defined steps for signing a message.
First, the sending agent generates a "Message/CPIM" object in accordance with the rules and formats specified in [MSGFMT].
Example 1: Sender generates "Message/CPIM" object:
| Content-type: Message/CPIM | | From: Juliet Capulet <im:juliet@example.com> | To: Romeo Montague <im:romeo@example.net> | DateTime: 2003-12-09T11:45:36.66Z | Subject: Imploring | | Content-type: text/plain; charset=utf-8 | Content-ID: <1234567890@example.com> | | Wherefore art thou, Romeo?
Once the sending agent has generated the "Message/CPIM" object, the sending agent may sign it. The result is a multipart [SMIME] object (see [MULTI]) that has a Content-Type of "multipart/signed" and includes two parts: one whose Content-Type is "Message/CPIM" and another whose Content-Type is "application/pkcs7-signature".
Example 2: Sender generates multipart/signed object:
| Content-Type: multipart/signed; boundary=next; | micalg=sha1; | protocol=application/pkcs7-signature | | --next | Content-type: Message/CPIM | | From: Juliet Capulet <im:juliet@example.com> | To: Romeo Montague <im:romeo@example.net> | DateTime: 2003-12-09T23:45:36.66Z | Subject: Imploring | | Content-type: text/plain; charset=utf-8 | Content-ID: <1234567890@example.com> | | Wherefore art thou, Romeo? | --next | Content-Type: application/pkcs7-signature | Content-Disposition: attachment;handling=required;\ | filename=smime.p7s | | [signed body part] | | --next--
The sending agent now wraps the "multipart/signed" object in an XML CDATA section, which is contained in an <e2e/> element that is included as a child element of the XMPP message stanza and that is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace.
Example 3: Sender generates XMPP message stanza:
| <message to='romeo@example.net/orchard' type='chat'> | <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'> | <![CDATA[ | Content-Type: multipart/signed; boundary=next; | micalg=sha1; | protocol=application/pkcs7-signature | | --next | Content-type: Message/CPIM | | From: Juliet Capulet <im:juliet@example.com> | To: Romeo Montague <im:romeo@example.net> | DateTime: 2003-12-09T23:45:36.66Z | Subject: Imploring | | Content-type: text/plain; charset=utf-8 | Content-ID: <1234567890@example.com> | | Wherefore art thou, Romeo? | --next | Content-Type: application/pkcs7-signature | Content-Disposition: attachment;handling=required;\ | filename=smime.p7s | | [signed body part] | | --next-- | ]]> | </e2e> | </message>
The following example illustrates the defined steps for encrypting a message.
First, the sending agent generates a "Message/CPIM" object in accordance with the rules and formats specified in [MSGFMT].
Example 4: Sender generates "Message/CPIM" object:
| Content-type: Message/CPIM | | From: Juliet Capulet <im:juliet@example.com> | To: Romeo Montague <im:romeo@example.net> | DateTime: 2003-12-09T11:45:36.66Z | Subject: Imploring | | Content-type: text/plain; charset=utf-8 | Content-ID: <1234567890@example.com> | | Wherefore art thou, Romeo?
Once the sending agent has generated the "Message/CPIM" object, the sending agent may encrypt it.
Example 5: Sender generates encrypted object:
| U2FsdGVkX19okeKTlLxa/1n1FE/upwn1D20GhPWqhDWlexKMUKYJInTWzERP+vcQ | /OxFs40uc9Fx81a5/62p/yPb/UWnuG6SR6o3Ed2zwcusDImyyz125HFERdDUMBC9 | Pt6Z4cTGKBmJzZBGyuc3Y+TMBTxqFFUAxeWaoxnZrrl+LP72vwbriYc3KCMxDbQL | Igc1Vzs5/5JecegMieNY24SlNyX9HMFRNFpbI64vLxYEk55A+3IYbZsluCFT31+a | +GeAvJkvH64LRV4mPbUhENTQ2wbAwnOTvbLIaQEQrii78xNEh+MK8Bx7TBTvi4yH | Ddzf9Sim6mtWsXaCAvWSyp0X91d7xRJ4JIgKfPzkxNsWJFCLthQS1p734eDxXVd3 | i08lEHzyll6htuEr59ZDAw==
The sending agent now wraps the encrypted object in an XML CDATA section, which is contained in an <e2e/> element that is included as a child element of the XMPP message stanza and that is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace.
Example 6: Sender generates XMPP message stanza:
| <message to='romeo@example.net/orchard' type='chat'> | <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'> | <![CDATA[ | U2FsdGVkX19okeKTlLxa/1n1FE/upwn1D20GhPWqhDWlexKMUKYJInTWzERP+vcQ | /OxFs40uc9Fx81a5/62p/yPb/UWnuG6SR6o3Ed2zwcusDImyyz125HFERdDUMBC9 | Pt6Z4cTGKBmJzZBGyuc3Y+TMBTxqFFUAxeWaoxnZrrl+LP72vwbriYc3KCMxDbQL | Igc1Vzs5/5JecegMieNY24SlNyX9HMFRNFpbI64vLxYEk55A+3IYbZsluCFT31+a | +GeAvJkvH64LRV4mPbUhENTQ2wbAwnOTvbLIaQEQrii78xNEh+MK8Bx7TBTvi4yH | Ddzf9Sim6mtWsXaCAvWSyp0X91d7xRJ4JIgKfPzkxNsWJFCLthQS1p734eDxXVd3 | i08lEHzyll6htuEr59ZDAw== | ]]> | </e2e> | </message>
In order to sign and/or encrypt presence information, a sending agent MUST use the following procedure:
<e2e/> child of a <presence/> stanza, where the <e2e/> element is
qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace. The
<presence/> stanza MUST include a 'to' attribute, i.e., it must
be an instance of directed presence as defined in [XMPP-IM].
The following example illustrates the defined steps for signing presence information.
First, the sending agent generates an "application/pidf+xml" object in accordance with the rules and formats specified in [PIDF].
Example 7: Sender generates "application/pidf+xml" object:
| <?xml version="1.0" encoding="UTF-8"?> | <presence xmlns="urn:ietf:params:xml:ns:pidf" | xmlns:im="urn:ietf:params:xml:ns:pidf:im" | entity="pres:juliet@example.com"> | <tuple id="hr0zny" | <status> | <basic>open</basic> | <im:im>away</im:im> | </status> | <note xml:lang="en">retired to the chamber</note> | <timestamp>2003-12-09T23:53:11.31</timestamp> | </tuple> | </presence>
Once the sending agent has generated the "application/pidf+xml"
object, the sending agent may sign it. The result is a multipart
[SMIME] object (see [MULTI]) that has a Content-Type of
"multipart/signed" and includes two parts: one whose Content-Type is
"application/pidf+xml" and another whose Content-Type is
"application/pkcs7-signature".
Example 8: Sender generates multipart/signed object:
| Content-Type: multipart/signed; boundary=next; | micalg=sha1; | protocol=application/pkcs7-signature | | --next | Content-type: application/pidf+xml | Content-ID: <2345678901@example.com> | | <xml version="1.0" encoding="UTF-8"?> | <presence xmlns="urn:ietf:params:xml:ns:pidf" | xmlns:im="urn:ietf:params:xml:ns:pidf:im" | entity="pres:juliet@example.com"> | <tuple id="hr0zny"> | <status> | <basic>open</basic> | <im:im>away</im:im> | </status> | <note xml:lang="en">retired to the chamber</note> | <timestamp>2003-12-09T23:53:11.31Z</timestamp> | </tuple> | </presence> | --next | Content-Type: application/pkcs7-signature | Content-Disposition: attachment;handling=required;\ | filename=smime.p7s | | [signed body part] | | --next--
The sending agent now wraps the "multipart/signed" object in an XML CDATA section, which is contained in an <e2e/> element that is included as a child element of the XMPP message stanza and that is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace.
Example 9: Sender generates XMPP presence stanza:
| <presence to='romeo@example.net/orchard'> | <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'> | <![CDATA[ | Content-Type: multipart/signed; boundary=next; | micalg=sha1; | protocol=application/pkcs7-signature | | --next | Content-type: application/pidf+xml | Content-ID: <2345678901@example.com> | | <xml version="1.0" encoding="UTF-8"?> | <presence xmlns="urn:ietf:params:xml:ns:pidf" | xmlns:im="urn:ietf:params:xml:ns:pidf:im" | entity="pres:juliet@example.com"> | <tuple id="hr0zny"> | <status> | <basic>open</basic> | <im:im>away</im:im> | </status> | <note xml:lang="en">retired to the chamber</note> | <timestamp>2003-12-09T23:53:11.31Z</timestamp> | </tuple> | </presence> | --next | Content-Type: application/pkcs7-signature | Content-Disposition: attachment;handling=required;\ | filename=smime.p7s | | [signed body part] | | --next-- | ]]> | </e2e> | </presence>
The following example illustrates the defined steps for encrypting presence information.
First, the sending agent generates an "application/pidf+xml" object in accordance with the rules and formats specified in [PIDF].
Example 10: Sender generates "application/pidf+xml" object:
| <?xml version="1.0" encoding="UTF-8"?> | <presence xmlns="urn:ietf:params:xml:ns:pidf" | xmlns:im="urn:ietf:params:xml:ns:pidf:im" | entity="pres:juliet@example.com"> | <tuple id="hr0zny" | <status> | <basic>open</basic> | <im:im>away</im:im> | </status> | <note xml:lang="en">retired to the chamber</note> | <timestamp>2003-12-09T23:53:11.31</timestamp> | </tuple> | </presence>
Once the sending agent has generated the "application/pidf+xml" object, the sending agent may encrypt it.
Example 11: Sender generates encrypted object:
| U2FsdGVkX18VJPbx5GMdFPTPZrHLC9QGiVP+ziczu6zWZLFQxae6O5PP6iqpr2No | zOvBVMWvYeRAT0zd18hr6qsqKiGl/GZpAAbTvPtaBxeIykxsd1+CX+U+iw0nEGCr | bjiQrk0qUKJ79bNxwRnqdidjhyTpKSbOJC0XZ8CTe7AE9KDM3Q+uk+O3jrqX4byL | GBlKThbzKidxz32ObojPEEwfFiM/yUeqYUP1OcJpUmeQ8lcXhD6tcx+m2MAyYYLP | boKQxpLknxRnbM8T/voedlnFLbbDu69mOlxDPbr1mHZd3hDsyFudb1fb4rI3Kw0K | Nq+3udr2IkysviJDgQo+xGIQUG/5sED/mAaPRlj4f/JtTzvT4EaQTawv69ntXfKV | MCr9KdIMMdjdJzOJkYLoAhNVrcZn5tw8WsJGwuKuhYb/SShy7InzOapPaPAl7/Mm | PHj7zj3NZ6EEIweDOuAwWlIG/dT506tci27+EW7JnXwMPnFMkF+6a7tr/0Y+iiej | woJxUIBqCOgX+U7srHpK2NYtNTZ7UQp2V0yEx1JV8+Y=
The sending agent now wraps the encrypted object in an XML CDATA section, which is contained in an <e2e/> element that is included as a child element of the XMPP message stanza and that is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace.
Example 12: Sender generates XMPP presence stanza:
| <presence to='romeo@example.net/orchard'> | <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'> | <![CDATA[ | U2FsdGVkX18VJPbx5GMdFPTPZrHLC9QGiVP+ziczu6zWZLFQxae6O5PP6iqpr2No | zOvBVMWvYeRAT0zd18hr6qsqKiGl/GZpAAbTvPtaBxeIykxsd1+CX+U+iw0nEGCr | bjiQrk0qUKJ79bNxwRnqdidjhyTpKSbOJC0XZ8CTe7AE9KDM3Q+uk+O3jrqX4byL | GBlKThbzKidxz32ObojPEEwfFiM/yUeqYUP1OcJpUmeQ8lcXhD6tcx+m2MAyYYLP | boKQxpLknxRnbM8T/voedlnFLbbDu69mOlxDPbr1mHZd3hDsyFudb1fb4rI3Kw0K | Nq+3udr2IkysviJDgQo+xGIQUG/5sED/mAaPRlj4f/JtTzvT4EaQTawv69ntXfKV | MCr9KdIMMdjdJzOJkYLoAhNVrcZn5tw8WsJGwuKuhYb/SShy7InzOapPaPAl7/Mm | PHj7zj3NZ6EEIweDOuAwWlIG/dT506tci27+EW7JnXwMPnFMkF+6a7tr/0Y+iiej | woJxUIBqCOgX+U7srHpK2NYtNTZ7UQp2V0yEx1JV8+Y= | ]]> | </e2e> | </presence>
The foregoing sections of this memo describe how to secure "least common denominator" messaging and presence data of the kind that can be directly translated into the MSGFMT or PIDF formats. However, XMPP possesses a third base-level stanza type (<iq/>) in addition to
<message/> and <presence/>, as well as the ability to include extended XML data within arbitrary child elements of the three core stanza types. Therefore, it would be desirable to secure such data if possible.
Because [MSGFMT] specifies the ability to encapsulate any MIME type, the approach taken in this memo is to include arbitrary XMPP data in an XML media type named "application/xmpp+xml" as specified more fully in Section 10 below.
The following examples illustrate the structure of the
"application/xmpp+xml" MIME type. (Note: The
'http://jabber.org/protocol/evil' namespace used in these examples is
associated with an April Fool's protocol written to be the instant
messaging equivalent of RFC 3514; it is included only as an instance
of extended information included in an XML stanza and should not be
taken seriously as a functional XMPP extension.)
Example 13: Message stanza with extended data contained in "application/xmpp+xml" MIME type:
| <?xml version='1.0' encoding='UTF-8'?> | <xmpp xmlns='jabber:client'> | <message | from='iago@example.com/pda' | to='emilia@example.com/cell'> | <body> | I told him what I thought, and told no more | Than what he found himself was apt and true. | </body> | <evil xmlns='http://jabber.org/protocol/evil'/> | </message> | </xmpp>
Example 14: Presence stanza with extended data contained in "application/xmpp+xml" MIME type:
| <?xml version='1.0' encoding='UTF-8'?> | <xmpp xmlns='jabber:client'> | <presence from='iago@example.com/pda'> | <show>dnd</show> | <status>Fomenting dissension</status> | <evil xmlns='http://jabber.org/protocol/evil'/> | </presence> | </xmpp>
Example 15: IQ stanza with extended data contained in "application/ xmpp+xml" MIME type:
| <?xml version='1.0' encoding='UTF-8'?> | <xmpp xmlns='jabber:client'> | <iq type='result' | from='iago@example.com/pda' | to='emilia@example.com/cell' | id='evil1'> | <query xmlns='jabber:iq:version'> | <name>Stabber</name> | <version>666</version> | <os>FiendOS</os> | </query> | <evil xmlns='http://jabber.org/protocol/evil'/> | </iq> | </xmpp>
Just as with the "Message/CPIM" and "application/pidf+xml" objects,
the "application/xmpp+xml" object would be signed and/or encrypted,
then encapsulated within an XML CDATA section (see Section 2.7 of
[XML]) contained in an <e2e/> child of a <presence/> stanza, where
the <e2e/> element is qualified by the
'urn:ietf:params:xml:ns:xmpp-e2e' namespace.
[SMIME] does not specify how to obtain a certificate from a certificate authority, but instead mandates that every sending agent must already have a certificate. The PKIX Working Group has, at the time of this writing, produced two separate standards for certificate enrollment: [CMP] and [CMC]. Which method to use for certificate enrollment is outside the scope of this memo.
A receiving agent MUST provide some certificate retrieval mechanism in order to gain access to certificates for recipients of digital envelopes. This memo does not address how S/MIME agents handle certificates, only what they do after a certificate has been validated or rejected. S/MIME certification issues are covered in [CERT].
However, at a minimum, for initial S/MIME deployment, a user agent SHOULD automatically generate a message to an intended recipient requesting that recipient's certificate in a signed return message. Receiving and sending agents SHOULD also provide a mechanism to allow a user to "store and protect" certificates for correspondents in such a way so as to guarantee their later retrieval.
End-entity certificates used by XMPP entities in the context of this memo SHOULD contain a valid instant messaging and presence address. The address SHOULD be specified as both an 'im:' URI (for instant messaging, as defined in [CPIM]) and a 'pres:' URI (for presence, as defined in [CPP]); each of these URIs SHOULD be specified in a separate GeneralName entry of type uniformResourceIdentifier inside the subjectAltName (i.e., two separate entries). Information in the subject distinguished name SHOULD be ignored.
Each URI MUST be of the form <im:address> or <pres:address>, where the "address" portion is an XMPP address (also referred to as a Jabber Identifier or JID) as defined in [XMPP-CORE], prepended with
the 'im:' or 'pres:' URI scheme. The address SHOULD be of the form
<node@domain> (i.e., a "bare JID"), although any valid JID form MAY be used.
The value of the JID contained in the XMPP 'from' attribute MUST match a JID provided in the signer's certificate, with the exception that the resource identifier portion of the JID contained in the 'from' attribute SHOULD be ignored for matching purposes.
Receiving agents MUST check that the sending JID matches a JID provided in the signer's certificate, with the exception that the resource identifier portion of the JID contained in the 'from' attribute SHOULD be ignored for matching purposes. A receiving agent SHOULD provide some explicit alternate processing of the stanza if this comparison fails, which may be to display a message informing the recipient of the addresses in the certificate or other certificate details.
The subject alternative name extension is used in S/MIME as the preferred means to convey the instant messaging and presence address that corresponds to the entity for this certificate. Any XMPP address present in the certificate MUST be encoded using the ASN.1 Object Identifier "id-on-xmppAddr" as specified in Section 5.1.1 of [XMPP-CORE].
Because it is expected that XMPP applications will not interface with older 7-bit systems, the transfer encoding (as defined in Section 3.1.2 of [SMIME]) MUST be "binary".
If a stanza is both signed and encrypted, it SHOULD be signed first, then encrypted.
If the sender and recipient are involved in an active messaging session over a period of time, the sending agent SHOULD include the sender's certificate along with at least one encrypted message stanza every five minutes. Outside the context of an active messaging session, the sending agent SHOULD include the sender's certificate along with each encrypted message stanza. A sending agent MAY include the sender's certificate along with each encrypted presence stanza. However, a sending agent SHOULD NOT include a certificate more than once every five minutes.
Sending agents SHOULD attach a signature to each encrypted XML stanza. If a signature is attached, a Content-Disposition header field (as defined in [DISP]) SHOULD be included to specify how the signature is to be handled by the receiving application.
If the receiving agent determines that the signature attached to an encrypted XML stanza is invalid, it SHOULD NOT present the stanza to the intended recipient (human or application), SHOULD provide some explicit alternate processing of the stanza (which may be to display a message informing the recipient that the attached signature is invalid), and MAY return a stanza error to the sender as described under Recipient Error Handling (Section 7).
If the receiving agent is unable to decrypt the encrypted XML stanza, it SHOULD NOT present the stanza to the intended recipient (human or application), SHOULD provide some explicit alternate processing of the stanza (which may be to display a message informing the recipient that it has received a stanza that cannot be decrypted), and MAY return a stanza error to the sender as described under Recipient Error Handling (Section 7).
Timestamps are included in "Message/CPIM" and "application/pidf+xml" objects to help prevent replay attacks. All timestamps MUST conform to [DATETIME] and be presented as UTC with no offset, including fractions of a second as appropriate. Absent a local adjustment to the sending agent's perceived time or the underlying clock time, the sending agent MUST ensure that the timestamps it sends to the receiver increase monotonically (if necessary by incrementing the seconds fraction in the timestamp if the clock returns the same time for multiple requests). The following rules apply to the receiving application:
All implementations MUST support the following algorithms. Implementations MAY support other algorithms as well.
For CMS SignedData:
For CMS EnvelopedData:
When an XMPP entity receives an XML stanza containing data that is signed and/or encrypted using the protocol described herein, several scenarios are possible:
Case #1: The receiving application does not understand the protocol.
Case #2: The receiving application understands the protocol and is able to decrypt the payload and verify the sender's signature.
Case #3: The receiving application understands the protocol and is able to decrypt the payload and verify the sender's signature, but the timestamps fail the checks specified above under Checking of Timestamps (Section 6.9).
Case #4: The receiving application understands the protocol and is able to decrypt the payload but is unable to verify the sender's signature.
Case #5: The receiving application understands the protocol but is unable to decrypt the payload.
In Case #1, the receiving application MUST do one and only one of the following: (1) ignore the <e2e/> extension, (2) ignore the entire stanza, or (3) return a <service-unavailable/> error to the sender, as described in [XMPP-CORE].
In Case #2, the receiving application MUST NOT return a stanza error to the sender, since this is the success case.
In Case #3, the receiving application MAY return a <not-acceptable/> error to the sender (as described in [XMPP-CORE]), optionally supplemented by an application-specific error condition element
<bad-timestamp/> as shown below:
Example 16: Recipient returns <not-acceptable/> error:
<message from='romeo@example.net/orchard' type='chat'>
<e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
[CDATA section here]
</e2e>
<error type='modify'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<bad-timestamp xmlns='urn:ietf:params:xml:xmpp-e2e'/>
</error>
</message>
In Case #4, the receiving application SHOULD return a
<not-acceptable/> error to the sender (as described in [XMPP-CORE]), optionally supplemented by an application-specific error condition element <unverified-signature/> as shown below:
Example 17: Recipient returns <not-acceptable/> error:
<message from='romeo@example.net/orchard' type='chat'>
<e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
[CDATA section here]
</e2e>
<error type='modify'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<unverified-signature xmlns='urn:ietf:params:xml:xmpp-e2e'/>
</error>
</message>
In Case #5, the receiving application SHOULD return a <bad-request/> error to the sender (as described in [XMPP-CORE]), optionally supplemented by an application-specific error condition element
<decryption-failed/> as shown below:
Example 18: Recipient returns <bad-request/> error:
<message from='romeo@example.net/orchard' type='chat'>
<e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
[CDATA section here]
</e2e>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<decryption-failed xmlns='urn:ietf:params:xml:xmpp-e2e'/>
</error>
</message>
A common method for achieving interoperability between two disparate services is through the use of a "gateway" that interprets the protocols of each service and translates them into the protocols of the other. The CPIM specifications (specifically [MSGFMT] and [PIDF] define the common profiles to be used for interoperability between instant messaging and presence services that comply with [IMP-REQS]. In the case of communications between an XMPP service and a non-XMPP service, we can visualize this relationship as follows:
+-------------+ +-------------+ +------------+ | | | | | | | XMPP | | XMPP-CPIM | | Non-XMPP | | Service | <----> | Gateway | <----> | Service | | | | | | | +-------------+ +-------------+ +------------+
The end-to-end encryption method defined herein enables the exchange of encrypted and/or signed instant messages and presence through an XMPP-CPIM gateway. In particular:
<e2e> and </e2e> tags), and then route the XMPP stanza to the XMPP
service.
The wrapped S/MIME object MUST be immutable and MUST NOT be modified by an XMPP-CPIM gateway.
The <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'/> element is a
wrapper for an XML CDATA section (see Section 2.7 of [XML]) that
contains a "Message/CPIM", "application/pidf+xml", or
"application/xmpp+xml" object. Thus the
'urn:ietf:params:xml:xmpp-e2e' namespace has no inherent semantics,
and the semantics of the encapsulated object are defined by one of
the following specifications:
Although the "application/xmpp+xml" media type is specified in this document, the <xmpp/> element is simply a wrapper for a <message/>,
<presence/>, or <iq/> stanza, where the semantics of those stanza types are specified in [XMPP-CORE].
Given that the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace has no inherent semantics and specifies a using protocol only, versioning is the responsibility of the protocols that define the encapsulated objects ([MSGFMT], [PIDF], and [XMPP-CORE]).
The "application/xmpp+xml" media type adheres to the guidelines specified in [XML-MEDIA]. The root element for this MIME type is
<xmpp/>, and the root element MUST contain one and only one child element, corresponding to one of the XMPP stanza types (i.e., message, presence, or iq) if the default namespace is 'jabber:client' or 'jabber:server' as defined in [XMPP-CORE]. The character encoding for this XML media type MUST be UTF-8, in accordance with Section 11.5 of [XMPP-CORE].
This entire memo discusses security. Detailed security
considerations for instant messaging and presence protocols are given
in [IMP-REQS] (Sections 5.1 through 5.4), and for XMPP in particular
are given in [XMPP-CORE] (Sections 12.1 through 12.6). In addition,
all of the security considerations specified in [XML-MEDIA] apply to
the "application/xmpp+xml" media type.
The end-to-end security method defined here MAY result in exchanging secured instant messages and presence information through a gateway that implements the CPIM specifications. Such a gateway MUST be compliant with the minimum security requirements of the instant messaging and presence protocols with which it interfaces.
A URN sub-namespace of signed and encrypted content for the Extensible Messaging and Presence Protocol (XMPP) is defined as follows. (This namespace name adheres to the format defined in [XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-e2e
Specification: RFC 3923
Description: This is an XML namespace name of signed and encrypted
content for the Extensible Messaging and Presence Protocol as
defined by RFC 3923.
Registrant Contact: IESG, <iesg@ietf.org>
To: ietf-types@iana.org
Subject: Registration of MIME media type application/xmpp+xml
MIME media type name: application
MIME subtype name: xmpp+xml
Required parameters: (none)
Optional parameters: (charset) Same as charset parameter of
application/xml as specified in RFC 3023; per Section 11.5 of
[XMPP-CORE], the charset must be UTF-8.
Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023; per Section 11.5 of
[XMPP-CORE], the encoding must be UTF-8.
Security considerations: All of the security considerations specified
in RFC 3023 and [XMPP-CORE] apply to this XML media type. Refer
to Section 11 of RFC 3923.
Interoperability considerations: (none)
Specification: RFC 3923
Applications which use this media type: XMPP-compliant instant
messaging and presence systems.
Additional information: (none)
Person and email address to contact for further information: IESG,
<iesg@ietf.org>
Intended usage: COMMON
Author/Change controller: IETF, XMPP Working Group
[CERT] Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.1 Certificate Handling",
RFC 3850, July 2004.
[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
3852, July 2004.
[CMS-AES] Schaad, J., "Use of the Advanced Encryption Standard
(AES) Encryption Algorithm in Cryptographic Message
Syntax (CMS)", RFC 3565, July 2003.
[CMS-ALG] Housley, R., "Cryptographic Message Syntax (CMS)
Algorithms", RFC 3370, August 2002.
[CPIM] Peterson, J., "Common Profile for Instant Messaging
(CPIM)", RFC 3860, August 2004.
[CPP] Peterson, J., "Common Profile for Presence (CPP)", RFC
3859, August 2004.
[DATETIME] Klyne, G. and C. Newman, "Date and Time on the
Internet: Timestamps", RFC 3339, July 2002.
[DISP] Troost, R., Dorner, S., and K. Moore, Ed.,
"Communicating Presentation Information in Internet
Messages: The Content-Disposition Header Field", RFC
2183, August 1997.
[IMP-MODEL] Day, M., Rosenberg, J., and H. Sugano, "A Model for
Presence and Instant Messaging", RFC 2778, February
2000.
[IMP-REQS] Day, M., Aggarwal, S., Mohr, G., and J. Vincent,
"Instant Messaging/Presence Protocol Requirements", RFC
2779, February 2000.
[MSGFMT] Klyne, G. and D. Atkins, "Common Presence and Instant
Messaging (CPIM): Message Format", RFC 3862, August
2004.
[MULTI] Galvin, J., Murphy, S., Crocker, S., and N. Freed,
"Security Multiparts for MIME: Multipart/Signed and
Multipart/Encrypted", RFC 1847, October 1995.
[PIDF] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr,
W., and J. Peterson, "Presence Information Data Format
(PIDF)", RFC 3863, August 2004.
[SMIME] Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.1 Message Specification",
RFC 3851, July 2004.
[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[XML-MEDIA] Murata, M., St. Laurent, S. and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[XMPP-CORE] Saint-Andre, P., Ed., "Extensible Messaging and
Presence Protocol (XMPP): Core", RFC 3920, October
2004.
[XMPP-IM] Saint-Andre, P., Ed., "Extensible Messaging and
Presence Protocol (XMPP) Instant Messaging and
Presence", RFC 3921, October 2004.
[CAPS] Hildebrand, J. and P. Saint-Andre, "Entity
Capabilities", JSF JEP 0115, August 2004.
[CMC] Myers, M., Liu, X., Schaad, J. and J. Weinstein,
"Certificate Management Messages over CMS", RFC 2797,
April 2000.
[CMP] Adams, C. and S. Farrell, "Internet X.509 Public Key
Infrastructure Certificate Management Protocols", RFC
2510, March 1999.
[DISCO] Hildebrand, J., Millard, P., Eatmon, R. and P. Saint-
Andre, "Service Discovery", JSF JEP 0030, July 2004.
[MUC] Saint-Andre, P., "Multi-User Chat", JSF JEP 0045, June
2004.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (3rd ed)", W3C
REC-xml, February 2004, <http://www.w3.org/TR/REC-xml>.
[XML-REG] Mealling, M., "The IETF XML Registry", BCP 81, RFC
3688, January 2004.
The following XML schema is descriptive, not normative.
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-e2e'
xmlns='urn:ietf:params:xml:ns:xmpp-e2e'
elementFormDefault='qualified'>
<xs:element name='e2e' type='xs:string'/>
<xs:element name='decryption-failed' type='empty'/>
<xs:element name='signature-unverified' type='empty'/>
<xs:element name='bad-timestamp' type='empty'/>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
Peter Saint-Andre
Jabber Software Foundation
EMail: stpeter@jabber.org
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